Any of conventional automobiles and motor-cycles is equipped with suspension devices between chassis and shaft via springs and shock-absorbers in order to relax swinging motion caused by differential steps or projections and recesses on the road surface or tilt in the course of making a turn thereby making it possible to perform stable run. However, any of conventional bicycles, tricycles, baby carriages, handcarts, or trucks being devoid of said suspension devices causes slight projections or recesses on the road to directly affect its body to cause the user to sense discomfort. In particular, any of those vehicles using small wheels devoid of pneumatic tires can not deal with slight differential steps or tilt to result in the difficulty to perform stable run.
For example, as shown in FIG. 12, an explanation is hereby given by way of exemplifying a two-wheeled handcraft 100 having an extremely simple-structured fixed shaft. A pair of wheels 106 is set to the left/right ends of a shaft 104, where a frame 102 with a handle is set to the upper part of the shaft 104, and yet, a bucket 108 is set to the frame 102. For example, when an operator carries a loaded bucket 108 by way of holding the frame 102 via the handle, he can deal with incline in the forward/backward direction (i.e., in the forwarding direction) on the road surface. However, if the road surface ever inclines in the leftward or rightward direction (being orthogonal to the forwarding direction), not only the wheels 106 and the bucket 108, but the load itself is also obliged to tilt as per the incline on the road surface to cause the load to fall off from the bucket to result in the failure to convey the load.
As is obvious from the above case, such a conventional two-wheeled handcraft having a fixed shaft can not totally balance itself in the left and right directions, and yet, since projections or recesses on the road surface directly affect the handcraft body, such a conventional handcraft has been limitedly usable for conveying load under a very slow conveying rate. Likewise, similar results are generated from most of those vehicles being devoid of suspension devices such as a baby carriage or a truck equipped with several units of two-wheels having a fixed shaft of the above kind.
Accordingly, inventors of the present invention followed up studies in order to provide a simplified buffer corresponding to such a vehicle being devoid of the above-cited suspension device or such a vehicle having difficulty to fix any conventional suspension device thereto and finally achieved conception that has led to materialization of a novel suspension device based on a crank-type shaft related to the invention.